CPU REGISTER FILE CIRCUIT

T.O. 31S5-4-308-l

TM 11-5805-663-14-13

NAVELEX 0967-464-0010

of sixteen arithmetic functions on two paral-

carry generator U41. Each ALU Ul, U11,

lel 16-bit words. One 16-bit word is from

U21, or U31 indicates a carry condition by

the CPU ALU input multiplexer circuit and

generating the X and Y outputs which are

the other 16-bit word is from the CPU reg-

routed to the respective X and Y inputs of

ister file circuit. Commands from the CPU

look-ahead carry generator U41. If ALU U31

microcode register circuit specify which

indicates a carry condition, look-ahead

logical or arithmetic function is to be per-

carry generator U41. ALU Ul, U11, U21,

formed on the two words by the CPU ALU

or U31 indicates a carry condition by gen-

circuit. The output of the CPU ALU circuit

erating the X and Y outputs which are

can be stored in the CPU transmit register

generator U41 generates CN08-N which is

circuit, CPU address register circuit, or

routed to ALU Ul1. If ALU Ull indicates a

CPU emulation instruction register circuit

carry condition, look-ahead carry generator

and/or the CPU register file circuit.

U41 generates CN12-N which is routed to

ALU Ul. If ALU Ul indicates a carry con-

5-210. Detail Analysis (see figure 20). The

dition, COUT-N is generated by ALU Ul

ALU portion of the circuit consists of ALU's

and routed to the CPU carry and overflow

Ul, U11, U21, and U31. Each ALU performs

circuit to indicate a carry condition.

16 binary arithmetic operations or 16 Boolean

(logical) operations on two 4-bit nibbles.

5-213. ALU's U1, U11, U21 and U31 gen-

The CPU ALU input multiplexer circuit gen-

erate LBOO-P through LBl5-P which are

erates YOOA-P through Y15A-P which are ap-

routed to the CPU address register circuit,

plied to the B inputs of the four ALU's Ul,

CPU transmit register circuit, CPU register

U11, U21, and U31. The CPU register file

file circuit, and CPU emulation instruction

circuit generates XOOS-P through Xl5S-P

which are applied to the A inputs of the four

also routed to the Bus Controller where they

ALU's Ul, U11, U21, and U31.

are used as mask bits when the Bus Con-

troller and CPU are handling interrupts.

5 - 2 1 1 . The CPU microcode register circuit

generates M28T-P through M3lT-P which

5-214. When two 16-bit words of equal

are applied to the S inputs of ALU U31 and

magnitude are applied to the A and B inputs

ALU U21. These inputs specify which one

of the ALU's Ul, U11, U21, and U31 and a

of the 16 arithmetic or logical operations

comparison operation is to be performed,

are to be performed. Drivers DRl through

each A = B output of the four ALU's Ul, Ull,

DR4 generate M28B-P through M31B-P which

U21, and U31 go high. The four A = B out-

are applied to the S inputs of ALU Ul and

puts are wire-anded together and ALU1-P is

ALU U11. These inputs specify which one

genera ted. ALU1-P is routed to the CPU

of the 16 arithmetic or logical operations is

control circuit to indicate equality.

to be performed. M32T-P from the CPU

microcode register circuit is applied to the

5 - 2 1 5 . CPU REGISTER FILE CIRCUIT.

M input of the four ALU's Ul, U11, U21,

and U31 and specifies whether an arithmetic

or logical operation is to be performed. If

5 - 2 1 6 . Genera 1. The CPU register file cir-

M32T-P is high, logical operations are per-

cuit consists of twelve 16-bit registers con-

formed and if M32T-P is low, arithmetic

structed from twelve 4-by-4 flip-flop arrays.

operations are performed.

The twelve registers consist of the program

counter (RO), seven general registers (Rl

5 - 2 1 2 . M28B-P, M29B-P, M31B-P and

through R7), status register (R8), instruction

M32T-P arc routed to the CPU carry and

overflow circuit and enables the circuit to

registers. Registers RO through RB are used

generate a carry. When performing arith-

internally for execution of the microcode

metic operations, the CPU carry and over-

program instructions. The CPU microcode

flow circuit generates CYIN-P when a carry

condition is indicated and it is applied to

registers and data IS writtten into or read

the Cn input of ALU U31 and look-ahead

from the CPU ALU circuit.

5-32